Rod and tube type thermostat with axial movable adjustment means



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ROD AND TUBE TYPE THERMUSTAT WI TH AX I AL MOVABLE ADJUSTMENT MEANS Filed June 14, 1965 4 Sheets-Sheet 1 WE: 41 mm g 7 in May 16, 1%? o. M. KENDGN ROD AND TUBE TYPE THERMOSTAT WITH AX] AL MOVABLE ADJUSTMENT MEANS 4 Sheets-Sheet 2 Filed June 14, 1965 mud May 16, W67 0. M KENDON 3 9 R01) AND TUBE TYPE THERMOST/XT WITH flXl/UJ MOVABLE ADJUSTMENT MEANS Filed June 14, 1965 4 Sheets-Shaer. 5

O. M. KENDON ROD AND TUBE TYPE THERMOS'IA'I WITH AXIAL May M5, W6?

MOVABLE ADJUSTMENT MEANS Filed June 14, 1965 4 Sheets-Sheet 4 United States Patent Office 3,320,387 Patented May 16, 1967 3 320 337 Ron AND TUBE TYrn THERMOSTAT wrTr-r AXIAL MQVABLE ADJUSTMENT lWEANS Gwen Murray Kendon, 1 Cecil St., Upper Hutt, Wellington, New Zealand Filed .lune 14, 1965, Ser. No. 463,687 1 Claim. (Cl. 200-137) This invention relates to thermostat switches of the type having the movable contact carried on a snap-action switch blade.

In the snap-action thermostat, a spring toggle swatch blade carrying a movable contact is mounted so that the spring of the switch blade is biased to move the movable contact in one direction with a snap action and upon sufficient force being exerted on the appropriate part of the switch blade causing deformation thereof eventually to cause the movable contact to move in the opposite direction with a snap action. The pressure is applied to the spring toggle switch blade at a particular point which will allow the desired snap action. However, at the point where a desired snap is still maintained there may be a greater temperature differential than desired to operate the switch between the off and the on positions. By moving the point at which the force is applied to the toggle switch blade this differential can be considerably reduced, but with the force applied by a non-resilient mechanism to the toggle switch blade the snap action is lost or at least reduced to such an extent as to be no longer useful.

It is an object of the present invention to provide a thermostat switch incorporating a spring toggle switch blade arranged to operate with a snap action with the force being applied to the spring toggle switch blade so that only a small temperature differential is required to operate the switch between the on and the otf positions while still preserving a satisfactory snap action for the movable contact.

It is a further object of the invention to position the operating components so that there is a minimum of flexing which would result in lost motion and thus reduce the sensitivity of the switch.

It is a further object of the invention to minimize lost motion by using a lever system having a common fulcrum with the switch blade.

It is a further object of the invention to minimize friction and lost motion by using a knife edge type fulcrum.

It is a further object of the invention to position the pressure transmitting points of the operating mechanism so that its flexing does not result in lost motion.

It is a further object of the present invention to provide a force transmitting means adapted to enlarge the movement of the thermostat rod to apply a greater movement to operate the switch blade.

It is a still further object of the present invention to provide a thermostat switch which is particularly suitable for use in electrical frying pans or similar domestic appliances and which will allow an operation within a limited differential of temperature to maintain a substantially constant cooking temperature. s It is a still further object of the present invention to provide a casing for a thermostat switch for use in a domestic appliance such as a frying pan which will obviate or minimize liquid spilled during the cooking process from entering through the casing and into the switch mechanism.

One preferred form of the invention will now be described with reference to the accompanying drawings, in which:

FIGURE 1 is a plan view of an inverted thermostat according to the invention,

FIGURE 2 is a cross section on the line FF of FIG- URE 1, with the cover in place,

FIGURE 3 is a section on the line G-G of FIGURE 1,

FIGURE 4 is a section on the line A-A of FIGURE 1,

FIGURE 5 is a section on the line BB of FIGURE 1,

FIGURE 6 is a section on the line CC of FIGURE 1,

FIGURE 7 is a section on the line DD of FIGURE 1, and

FIGURE 8 is an end view the line EE of FIGURE 1.

Referring to the drawings, a molded plastic body or housing 1 is provided with recesses 2 adapted to receive female contact members 3 and 4 to engage with the terminals of the heating element of the frying pan or the like utensil. The housing also contains a chamber 5 in which a metal frame member 6 islocated, and the frame member has brazed thereto at 7 a thermostat tube 8 of brass or other suitable metal having an adequate c0- eflicient of expansion. Concentric with the tube 8 is a thermostat rod 9 brazed at iii to the swaged end of the tube 8. The rod is of a metal which is of a low coefficient of thermal expansion for example 36/64 nickel/ iron alloy and since the tube 8 is of a metal such as brass which has quite a high coefficient of thermal expansion, the tube expands and the end of the rod moves towards the end which is brazed at 7 to the metal frame member 6.

A mounting plate or support member 11 is sliclable on the surfaces of protuberances 48 of a cover 47 (to be referred to later), and the surfaces of protuberances 49 extending from bases 50 (see FIGURE 6). The support 11 is also slidably confined between guiding surfaces 13 of the body 1 and thus is insulated from the frame member 6.

The support member 11. carries an insulated post or abutment M against which bears a rotatably adjustable rod 15 threaded in the frame member 6 and rotatable through a boss 16 by a knob 17 providing an adjustment member operable from external-1y of the body 1. In other words, rotation of knob 17 will impart axial movement to the rod 15, and hence to the frame member 6. A su table scale (not shown) is disposed adjacent the knob 17. The knob 17 Carries a projection 18 which bears against stops 19 (FIGURE 7) to limit the movement of the knob 17. A spring 2G is provided between the frame member 6 and the boss 16 to obviate or minimize end play. Thus, the position assumed by the frame member 6 is adjustable by rotating the knob 17.

The support member 11 has threaded therein a necked screw 21 providing a support for a switch blade 22 of 3 suitable material such as beryllium copper. The trident switch blade carries a movable switch contact 23 at the end thereof remote from the screw 21. The necked screw 2]. passes through a suitable aperture in the switch blade. Part of the edge of the aperture engages in the neck of the screw to support the switch blade.

The movable contact 23 bears, when appropriately actuated against a fixed contact 24, which is held on the support member 11 by a screw 25 and nut 26 but is insulated from the support member if the post or abutment 14 and by an insulating member 27. A connector 28 and a wire 29 complete the circuit to the female contact member 4 as shown in FIGURE 1.

The thermostat is connected by a usual three core flex 30 to a three pin plug in the normal way and phase lead 31 of the flex is connected by a screw 32 to the support member 11. Since the switch blade 22 is in electrical contact with the support member 11 when the movable contact 23 makes contact with the fixed contact 24, there is a connection from the phase lead 31 through the abovementioned connections to one of the female contact members 4. A neon indicating light 33 is positioned relative looking in the direction of to an aperture 34 in the body 1 and is connected to lightup when the switch is in the on position.

A neutral lead 35 from the flex 30 is connected directly to the remaining female contact member 3 and a ground lead 36 is connected to a part of the frame member 6 by an appropriately positioned screw.

Returning to the switch blade, a switch spring 37 is provided by cutting a U shaped outline from the switch blade and the spring 37 is bowed in use with edge 40 in contact with a spring abutment 38 extending from the top of the support plate. This abutment and the necked screw are arranged so that the spring 37 is bowed with a line or bar contact between the edge 40 of the spring 37 and a depression of the abutment 38 so that, as shown in FIGURE 2, a line and consequently a low friction contact is obtained. As will be seen, the spring abutment has the face adapted to engage with the edge of the spring blade 37 provided as a wide V in cross section.

The switch blade is operable through a pressure means formed as a bell crank member 41 adapted to transmit the pressure caused by the movement of the thermostat rod relative to the tube to be applied to the switch blade. The switch blade is riveted by two rivets 42 to the bell crank member and the bell crank member carries two protuberances 43 which bear against the switch blade and thus provide pressure transmitting points to engage the switch blade. The protuberances are positioned on the bell crank member 41 at a position remote from the fixing thereof to the switch blade 22.

The arm of the bell crank member extending forwardly from the point of attachment of the switch blade 22 is a stifliy resilient arm which has some flexibility but which will in use transmit sufficient force to the switch blade to cause the operation thereof. The force is transmitted through the protuberances 43 and the line at which this force is applied has a material effect upon the operation of the switch. Each toggle switch blade has an optimum point of operation where the best results would be obtained if the force applied to the switch blade 22 was transmitted through a rigid body and movement from this point towards the contact has two effects. First, the differential between the operating temperature at which the contacts open and close is reduced which for most purposes and particularly for use in domestic heating appliances is advantageous. However, if the force was still applied through a rigid member, this advantage would be gained at the loss of the snap action. The applicant has found that where the bell crank member 41 is made from a material having some flexibility for example beryllium copper 0.028 inch thick, the deformation of the arm as the force is applied to the switch blade may be used to assist in enlarging the snap action as the switch operates. This of course is caused by the lessening of the deformation of the stiffly resilient arm as the switch blade operates to open the switch. Thus, the point at which the protuberances 43 transmit the force is such that the differential between the operating temperatures of the thermostat switch is only a few degrees. However, even with this small differential because of the resiliency of the stiffly resilient arm a sufficient snap action is retained. Of course, as will be realized materials having equivalent characteristics to the beryllium copper could be used for the bell crank member 41.

The bell crank has a further protuberance 44 acting as an abutment on the abutment arm and against which an insulating cap 45 bears. The insulating cap 45 in turn is a pressure transmitting member for transmitting pressure from the thermostat rod 9 to the protuberance 44 and thus to the bell crank member 41.

By this construction, movement of the rod 9 relative to the frame member 6 is transmitted to the switch blade 22 through the protuberances 43 in such a manner that the switch blade is moved to a position in which the spring of the switch blade assists such movement and snaps the switch to open position. During cooling, the increase of pressure results from the thermostat tube and rod in the switch blade moving to a further position in which the spring assists further movement and snap the switch to the closed position. This construction has the advantage that if the thermostat is turned back to the (off) position when the outer tube 8 is hot, the support member 11 will merely move away thus releasing tension on the switch blade so it cannot cause any damage to the switch mechanism. When the tube 8 is cold and the knob 17 is turned to the maximum setting, considerable flexing of the switch blade 22 is possible without damage to the apparatus while allowing ample sensitivity to provide for a low differential between the (on) and (off) positions of the thermostat switch during its maintenance of the cooking appliance, such as a frying pan, near its set temperature as above described.

Also, the points of contact between the pressure transmitting point, that is, the protuberance 44 on the abutment arm of the bell crank member 41 and the end of the cap 45 attached to the thermostat rod 9, and the end of the rod 15 and the abutment end of the support member 11 are substantially on the longitudinal center line of the thermostat tube 8 and the center line through the support member 11. In this way, any flexing of the components which may reduce the sensitivity of the thermostat is reduced.

To further compensate for the movement of the components which may vary the operation of the switch, the point 44 is provided by a rounded protuberance arranged to bear against a flat surface on the cap 45. Also, the point on the end of the rod 15 is rounded and bears against the flat surface of the frame member 6. In this way, if due to the clearance provided for the frame member 6 in the body 1 a slight slewing or rotary movement is possible, the radiused ends bearing against the flat surfaces tend to compensate for this slightly increased length through the frame member 6. This of course would only be a minute measurement in practice but it is a factor which contributes to the efficient operation of the switch.

A cover 47 is provided and the cover carries the protuberances 48 on which the support member 11 slides during its movement. The body 1 also is provided with projections 49a which engage the edges of apertures 50a in the frame member 6 to fix such member in the body 1. By this arrangement of protuberances on the body and cover, relative movement of the support member 11 and fixing of the frame member 6 is readily attained in a simple, yet effective fashion.

The cover 47 fits on a ledge 51 (FIGURE 6) and since the cover is fitted below the body 1, the edge of the body 1 near the cover lies below the mechanism so that splashes of fat, water or the like from the frying pan or similar utensil will normally be unable to enter within the body 1 due to the shape of the body. In addition, on the edge of the housing near the thermostat tube, a drip groove or gutter may be provided to carry away any drips or any other accumulation of water which may collect on the housing from the terminals of the appliance, the thermostat tube or the thermostat mechanism within the housing. The cover 47 is held in place with four or a requisite number of screws. A cord grip 53 (FIGURE 1) is provided and comprises a strip of metal held in place by two screws. Appropriate apertures 55 are provided and through which the female contact members 3 and 4 may be contacted by the prongs of the cooking appliance.

The use of the foregoing appliance is as follows: The thermostat is plugged in the known way to a cooking appliance, such as a frying pan with the prongs thereof contacting the female contact members 3 and 4 and the tube 8 of the thermostat is engaged in a socket in the body of the frying pan. The user will have rotated the knob 17 to an appropriate temperature and as a result, the support member 11 will be moved towards the cap 45 and during such movement the protuberance 44 will bear against the cap 45, the bell crank member 41 will pivot on the edge 54 of the switch blade 22 which bears against the neck 46, the protuberances 43 will'move in a direction such that the movable contact 23 will be moved towards the contact 24 until a position is reached in which the spring 37 augments such movement and press the contact 23 against the contact 24. If the tube 8 is cold, then such movement of the knob 17 will cause the switch plate 22 to flex considerably thereby applying considerable pressure between the contacts. This, however, is not harmful since the pressure is dependent only on the flexing of the switch blade.

If heat is applied to the thermostat tube by the heating of the frying pan, the tube 8 will lengthen and as a result due to the rod 9 only lengthening a lesser amount, the cap 45 will be moved away from the protuberance 44. This results in the pressure on the protuberance 44 lessening and, the switch blade 22 will flex to a lesser degree until a stage is reached when the blade moves to the same side of the line of contact 40 as that of the bow of the spring 37. As a result, the contact will open with a snap action and this opening will be caused by the spring 37 tending to move the contacts 23 and 24 away from each other. The pan will then cool until a stage is reached in which the above cycle is repeated with the snap action assisted by the stiffly resilient arm as above described and consequently, the spring operates to close the contacts again. However, by resetting the knob 17 appropriately, the contacts will open and close at a different range of operation. In this way, an extremely effective thermostat is arranged which may be provided in an extremely small casing and yet be effective and reliable in operation.

The invention is not to be confined to any strict conformity to the showing in the drawings but changes or modifications may be made therein so long as such changes or modifications mark no material departure from the spirit and scope of the appended claim.

What we claim is:

A thermostat switch comprising a thermostat body, a frame member positioned in said body, a thermostat tube secured to said frame member and extending from said body, a thermostat rod within said tube having a diiferent coefficient of thermal expansion from that of said tube, means fixing said rod to said tube at the end thereof remote from said body for constituting a thermostat rod and tube assemblage, a movable support member within said body, a manual operable control means mounted in said body opposite said tube, operating axial adjusting means for adjusting the position of said support member toward and away from said rod mounted in said tube, a fixed contact for said support member located at a distance remote from said rod and tube assemblage, a spring-toggle switch blade mounting means carried by said support means adjacent the end of said rod within said body, a spring-toggle switch blade having a movable contact for cooperation with said fixed contact, means mounting said switch blade on said spring-toggle switch blade mounting means, an abutment for a spring of said switch blade mounting means mounted on said support means, said spring-toggle switch blade mounting means and said abutment for the spring being so arranged that the spring of said switch blade is biased for moving the movable contact in one direction with a snap action and upon sufficient force being exerted on said switch blade for causing deformation thereof for ultimately causing said movable contact to move in the other direction with a snap action, a bell crank member having a stiffiy resilient arm attached to said switch blade in proximity to said spring-toggle switch blade mounting means with said resilient arm extending over said switch blade and having pressure transmitting points adjacent the end thereof for transmitting force to the switch blade adjacent the abutment means, said bell crank member also being provided with an abutment arm of shorter length than the length of said stiffly resilient arm and having a pressure transmitting point thereon adapted to be engaged by the end of said thermostat rod, the adjustment of said manually operable control efiecting sliding of said support member toward or away from the end of said rod thereby varying the distance through which said rod must be moved due to temperature change prior to the rod applying such pressure to the abutment arm as to cause operation of said movable contact thus varying the temperature setting of the thermostat by operation of said manually operable control, with an increase in temperature of said tube causing said rod to move away from said bell crank member under spring pressure from said spring-toggle switch blade mounting means following the movement of said rod and with said resilient arm deforming under the release of pressure due to the movement away of said rod, said switch blade following the pressure points of said bell crank member until the spring action thereof operates the movable contact with a snap action to open the switch and during cooling of the thermostat, an increase of pressure caused by movement of said rod toward said bell crank member causing said bell crank member to move for applying pressure to said switch blade with said resilient arm flexing under such pressure until the pressure build-up is sufficient for causing the switch blade to change its position to close the movable contact on to the fixed contact with a snap action and the pressure points follow said switch blade loss of flexing in said resilient arm.

References Cited by the Examiner V UNITED STATES PATENTS 3,069,916 12/1962 Watson 20067 XR 3,079,480 2/1963 Loveland 200137 BERNARD A. GILHEANY, Primary Examiner. H. A, LEWITTER, Assistant Examiner. 

